Sure, but I am trying to understand the statement, so I searched British Newspaper Archives for the word "blurred" and got an article about a blurred text and another about a blurred name - and in both these someone was trying to "decipher" some letters. So I searched

blurred decipher

only in 1888 and got some articles about people trying to decipher blurred texts and letters.

So from this empirical pilot we could hypothesize that Swansons statement has to do with a blurred text in Goulston Street and policemen trying to decipher it.

Decipher, meaning:

"to ​discover the ​meaning of something written ​badly or in a ​difficult or ​hidden way:
Can you decipher the writing on this ​envelope?"